hdabb 7451683 1.downloads.hindawi.com/journals/abb/2020/7451683.pdf · [4]. the complex interaction...

Review ArticleKnee Joint Biomechanics in Physiological Conditions and HowPathologies Can Affect It: A Systematic Review

Li Zhang ,1 Geng Liu ,1 Bing Han ,1 Zhe Wang ,1 Yuzhou Yan ,1 Jianbing Ma ,2

and Pingping Wei3

1Shaanxi Engineering Laboratory for Transmissions and Controls, Northwestern Polytechnical University, Xi'an 710072, China2Hong-Hui hospital, Xi’an Jiaotong University College of Medicine, Xi'an 710054, China3State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi'an 710054, China

Correspondence should be addressed to Geng Liu; [email protected]

Received 8 November 2019; Accepted 1 February 2020; Published 4 April 2020

Academic Editor: Stefano Zaffagnini

Copyright © 2020 Li Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, whichpermits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The knee joint, as the main lower limb motor joint, is the most vulnerable and susceptible joint. The knee injuries considerablyimpact the normal living ability and mental health of patients. Understanding the biomechanics of a normal and diseased kneejoint is in urgent need for designing knee assistive devices and optimizing a rehabilitation exercise program. In this paper, wesystematically searched electronic databases (from 2000 to November 2019) including ScienceDirect, Web of Science, PubMed,Google Scholar, and IEEE/IET Electronic Library for potentially relevant articles. After duplicates were removed and inclusioncriteria applied to the titles, abstracts, and full text, 138 articles remained for review. The selected articles were divided into twogroups to be analyzed. Firstly, the real movement of a normal knee joint and the normal knee biomechanics of four kinds ofdaily motions in the sagittal and coronal planes, which include normal walking, running, stair climbing, and sit-to-stand, werediscussed and analyzed. Secondly, an overview of the current knowledge on the movement biomechanical effects of commonknee musculoskeletal disorders and knee neurological disorders were provided. Finally, a discussion of the existing problems inthe current studies and some recommendation for future research were presented. In general, this review reveals that there is noclear assessment about the biomechanics of normal and diseased knee joints at the current state of the art. The biomechanicsproperties could be significantly affected by knee musculoskeletal or neurological disorders. Deeper understanding of thebiomechanics of the normal and diseased knee joint will still be an urgent need in the future.

1. Introduction

Since the number of the old and obese worldwide has beenincreasing yearly, the research on human motion dysfunc-tion is getting more and more attention. The knee joint, asthe main lower limb motor joint, is the most vulnerableand susceptible joint [1]. Knee impairments are the com-mon physical problems which impact the normal livingability and mental health of these patients [2]. The influ-ences mainly contain the supporting body weight, the assist-ing lower limb swing, and the absorbing strike shock [3].The movement biomechanics, as an important branch ofbiomechanics, studies the coordination of the bones, mus-cles, ligament, and tendons in various human movements[4]. The complex interaction of these structures allows the

knee to withstand tremendous forces during various normalmovements [1]. Therefore, it is an urgent need to study themovement biomechanics of the normal and diseased kneejoint for the assistance or rehabilitation of human locomo-tor function.

In the last decade, several related review papers appearedand could be divided into two aspects, normal knee biome-chanics and diseased knee biomechanics. For the former,Masouros et al. [5] analyzed the knee kinematics andmechanic and surrounding soft tissue in detail. The researchpointed out that the knowledge of these structures was veryuseful for the diagnosis and evaluations of treatment. Wanget al. [6] reviewed the modeling and simulation methods ofhuman musculoskeletal systems. The knee kinematics andkinetics in six common motions including walking, jogging,

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stair ascent, stair descent, squatting, and kneeling were dis-cussed. Chhabra et al. [1] reported the anatomic structuresand their relationships in the uninjured knee joint, whichprovided the critical guidance for the reconstruction of themultiple ligament injured knee joint. Madeti et al. [4] dis-cussed various model formulations of the knee joint, includ-ing mathematical, two-dimensional, and three-dimensionalmodels. And the forces acting on the knee joint had alsobeen compared. For the latter, Flandry et al. [7] providedan overview of the surgical anatomy of the knee joint andemphasized connective tissue structures and common injurypatterns. Woo et al. [8] reviewed the biological and biome-chanical knowledge of normal knee ligaments, as well asthe anatomical, biological, and functional perspectives ofthe current reconstruction knowledge following knee liga-ment injuries. The research also provided guidance forimproving the treatment of knee ligament injuries. Louwet al. [9] assessed the effects of the occluded vision on theknee kinematics and kinetics during functional activities,such as squatting, stepping down, drop landing, hopping,and cutting movements in healthy individuals and theindividuals with anterior cruciate ligament injury or recon-struction. Sosdian et al. [10] discussed the effects of kneearthroplasty on the kinematics and kinetic properties ofthe frontal plane and sagittal plane during the stancephase of normal walking. The results showed that the peakknee adduction angle and moment were decreased, but thepeak knee flexion moment was increased after kneearthroplasty. However, to our knowledge, there is noreview that synthesized the literature discussing the move-ment biomechanics of both the normal and the diseasedknee joint.

Understanding the knee biomechanics is a prerequisitefor designing knee assistive devices and optimizing rehabil-itation exercises. This paper provides an overview of thecurrent biomechanical knowledge on normal and injuredknee joints. For better assessment of the function of theknee joint, the biomechanical parameters including angle,moment, power, and stiffness from various researchers indifferent daily motions are reviewed and compared. Forbetter understanding the kinematics and kinetics of realknee movement, the polycentric rotation in the sagittalplane and biomechanics in the coronal plane are also dis-cussed. Further, the common knee disorders includingmusculoskeletal and neurological disorders and theirinfluences on the knee biomechanics are also reviewedand discussed. We hypothesized that the comprehensiveunderstanding of the knee joint biomechanics in physiolog-ical and pathological conditions could significantly improvethe design of knee assistive devices and rehabilitationexercise programs.

The rest of this paper is organized as follows. In Section 2,the search strategies adopted for the literature review areprovided. In Section 3, the selected literatures includingthe biomechanical properties of normal knee joint andthe knee diseased effects on the biomechanics are summa-rized. In Section 4, the limitations of the current studiesare briefly discussed and the recommendations for futureresearch are provided.

2. Methods

This review was conducted in accordance with PreferredReporting Items for Systematic Reviews and Meta-Analyses(PRISMA) [11]. We systematically searched electronic data-bases including ScienceDirect, Web of Science, PubMed,Google Scholar, and IEEE/IET Electronic Library for poten-tially relevant articles. The following terms were used as key-words (identical for all databases): “knee joint,” “gait,” “kneebiomechanics,” “knee disease,” and “sports biomechanics.”Given the fast advancement in acquisition equipment andtheoretical research of knee biomechanics, the search timerange was set from 2000 to November 2019. A total of 1787articles were retrieved initially. The daily life activities weremainly considered in this review, the articles about morecomplex activities, such as squats, hops, cut manoeuvres,were excluded. After 679 articles were excluded, 1108 articlesabout daily life activities were selected. In addition, review ofall references cited by the selected articles and more insightinto other relevant authors’ studies yielded an additional 35articles for possible inclusion. Then, all selected articles wereinput into Excel to eliminate duplicates. After 511 duplicateswere removed, 632 articles were assessed for inclusion.

Studies were considered eligible if they met the followinginclusion criteria: normal knee kinematics related, normalknee dynamics related, diseased knee kinematics related, dis-eased knee dynamics related, English, and full-text articles.Two reviewers (LZ and ZW) independently assessed the titleand abstracts of the potential studies. After an initial deci-sion, the full text of the studies that potentially met theinclusion criteria were assessed before a final decision wasmade. A senior reviewer (GL) was consulted in cases involv-ing disagreement. After exclusion of irrelevant titles andscreening of abstracts, 203 articles remained. Subsequently,detailed full-text screening based on the inclusion criteriawas carried out, and 65 articles were excluded. Finally, 138full-text articles were examined for full review. The searchprocess is demonstrated using the following diagram shownin Figure 1.

3. Results

We divided the 138 selected articles, which fulfilled the liter-ature search inclusion criteria, into two groups: biomechani-cal properties of normal knee joint and biomechanicalproperties of diseased knee joint. For the former, the realmovement of a normal knee joint and the normal knee bio-mechanics of four kinds of daily motions in the sagittal andcoronal planes, which include normal walking, running,stair climbing, and sit-to-stand, were discussed and ana-lyzed. For the latter, an overview of the current knowledgeon the movement biomechanical effects of common kneemusculoskeletal disorders (KOA) and knee neurologicaldisorders (SCI, stroke, and CP) were provided.

3.1. Biomechanical Properties of Normal Knee Joint

3.1.1. Knee Biomechanics of Daily Motions in Sagittal Plane.Walking, running, stair climbing, and sit-to-stand are veryfrequent motions in human’s daily life. In all of the motions,

2 Applied Bionics and Biomechanics

the main functions of the knee joint include supportingthe body weight (BW), absorbing shock of heel strikes,and assisting lower limbs swing [3]. According to the pre-vious researches, the passive knee flexion could reach160 deg in the sagittal plane [1, 5, 12]. The peak loadthrough the knee joint is 2-3 BW during walking, 2-5BW during sit-stand-sit, 4-6 BW during stair climbing,and 7-12 BW during running [12–14]. In this section, theROM, maximum moment, maximum power, and stiffnessof the knee joint are mainly discussed because they are thekey indexes for the design of knee assistive device and opti-mization of rehabilitation exercises.

As shown in Figure 2(a), the walking gait can be dividedinto two main phases: stance (about 0-65% of gait) and swingphases (about 65-100% of gait) [15, 16]. The stance phaseconsists of three subphases: initial (heel strike to foot flat),middle (foot flat to opposite heel strike), and terminal stance(opposite heel strike to toe off) [16, 17]. The knee joint in thestance phase is regarded as a shock damping mechanism toaccept the BW [18]. The swing phase consists of two sub-phases: initial (toe off to knee maximum flexion) and termi-nal swing (knee maximum flexion to heel strike) [16, 17].The main function of the knee in the swing phase is assistingflexion-extension for toe clearance, foot placement, and tak-ing over the load in the next step [19, 20]. Zheng [21]reported that the knee biomechanics is affected mainly bywalking speed. With the speed increased, the ROM, maxi-mum extension moment, and maximum absorption powerwould increase. Figure 2(b) shows the typical knee angle-time curve. There are two peak flexion (A and C) and exten-sion (B and D) angles. Points A and B occur in the stancephase, and C and D occur in the swing phase. Comparingthe two peak flexion angles, the value in the swing phase isalways greater than that in the stance phase. Table 1 givesthe values of these points from 18 studies. The ranges of

points A, B, C, and D are from 6 to 28 deg, -2 to 5 deg, 53to 78 deg, and -5 to 16 deg, respectively. In general, theROM is around 53 to 75 deg for normal walking.Figure 2(c) shows the typical knee moment-time curve. Thereare two peak extension (E and G) and flexion (F and H)moments. Point H occurs in the swing phase and the othersoccur in the stance phase. Table 2 gives the values of thesepoints from 11 studies. The values of these points vary consid-erably between different studies. The ranges of points E, F, G,and H are from 0.129 to 0.945Nm/kg, -0.675 to 0.067Nm/kg,0.101 to 0.466Nm/kg, and -0.420 to 0.086Nm/kg, respec-tively. The first peak extensionmoment is always greater thanthe second. But it is hard to determine who is bigger betweenthe two peak flexion moments. In general, the range ofmoment is about 0.458 to 1.265Nm/kg for normal walking.Figure 2(d) shows the typical knee power-time curve. Itincludes one peak generation power (J) and three peakabsorption powers (I, K, and L). Point L occurs in the swingphase and the others occur in the stance phase. For the kneejoint, there is only absorption power in the swing phase.And in the whole gait cycle, knee absorption powers are muchlarger than generation powers. Mooney and Herr [22] foundthat the mean net knee power is about -18W (mean genera-tion and absorption power is about 18W and -36W, respec-tively). Table 3 gives the values of these points from 10studies. The ranges of points I, J, K, and L are from -1.736to -0.116W/kg, 0.286 to 0.834W/kg, -1.935 to -0.403W/kg,and -2.712 to -0.321W/kg, respectively. In general, the rangeof power is about 1.035 to 3.214W/kg for normal walking.

As shown in Figure 3(a), the running cycle can be dividedinto four main phases: stance (heel strike to toe off), first float(toe off to opposite heel strike), swing (opposite heel strike toopposite toe off), and second float phases (opposite toe off toheel strike) [14]. The knee main function in running is simi-lar to that in walking. Comparing Figures 2 and 3, it can be

Records indentified throughdatabase searching

(n = 1787)

Additional records identified through other sources

(n = 38)

Duplicates removed (n = 1143)

Records excluded (n = 511)

Title and abstract review (n = 632)

Full-text articles for eligibility (n = 203)

Studies included in systematic review (n = 138)

Title and abstract excluded, with reasons (n = 429)

Full-text articles excluded, with reasons (n = 65)

Iden

tifica

tion

Scre

enin

gEl

igib

ility

Incl

uded

Complex activities excluded (n = 679)

Selected articles (n = 1108)

Figure 1: The PRISMA flow diagram of study selection process.

3Applied Bionics and Biomechanics

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Figure 2: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for a walking gaitcycle. (a) Sketch map of walking motion [14]. (b) Knee angle-time curve ((A) first peak knee flexion angle, (B) first peak kneeextension angle, (C) second peak knee flexion angle, and (D) second peak knee extension angle). (c) Knee moment-time curve ((E) firstpeak knee extension moment, (F) first peak knee flexion moment, (G) second peak knee extension moment, and (H) second peak kneeflexion moment). (d) Knee power-time curve ((I) first peak knee absorption power, (J) first peak knee generation power, (K) second peakknee absorption power, and (L) third peak knee absorption power) [16, 17].

Table 1: Overview over the experimental results of knee angle for normal walking.

StudySubjects (mean height ± SD (m),

meanweight ± SD (kg))Speed (m/s) A (°) B (°) C (°) D (°) C-A (°) ROM (°)

Collins et al. [125] 9 (1:84 ± 0:10, 77:4 ± 9:2) 1.25 12 3 61 -5 49 66

Zheng [21] 1 (1.78, 70) 1.2 22 10 66 6 44 60

Wang [126], Lee et al. [17] 1 (1.69, 63.5) 1.5 7 3 53 -2 46 55

Mooney and Herr [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 28 5 78 4 50 74

Shamaei et al. [3, 127] 3 (1:76 ± 0:75, 68:6 ± 2:2) 1.25 26 15 69 6 43 63

Blazkiewicz [128] 1 (1.85, 80) — 10 -2 53 0 43 55

Sridar et al. [34] 3 (1:70 ± 0:05, 74:7 ± 8:4) 1.0 22 11 62 2 40 60

Knaepen et al. [129] 10 (1:82 ± 0:10, 77:5 ± 11:7) 0.69 14 8 62 8 48 54

Shirota et al. [130] 4 (1:80 ± 0:08, 74 ± 6:8) 1.24 13 5 65 1 52 64

Gordon et al. [131] 3 (1:80 ± 0:01, 96 ± 9) 1.0 6 0 55 16 49 55

Ding et al. [132] 8 (1:76 ± 0:06, 78:5 ± 9:9) 1.25 24 7 75 0 51 75

Winter [133], Li et al. [134] 1 (—, 58) 1.3 16 5 67 -2 51 69

Beyl et al. [135] — — 22 8 64 1 42 63

Baliunas et al. [136] 15 (1:68 ± 0:12, 74 ± 16) 0.98 17 3 60 -2 43 62

Yang et al. [137] 1 (1.75, 70) 1.0 14 3 56 6 42 53

A: first peak knee flexion angle; B: first peak knee extension angle; C: second peak knee flexion angle; D: second peak knee extension angle.


observed that the curves of angle, moment, and power inrunning are also similar to that in walking. Hamner and Delp[23] reported that the knee biomechanics is mainly affectedby running speed. With increasing speed, the ROM, maxi-mum extension moment, and maximum absorption powerwould increase. Figure 3(b) shows the typical knee angle-time curve in a gait cycle and Table 4 gives the angles ofpoints A, B, C, and D from 7 studies. The ranges of pointsA, B, C, and D are from 36 to 60 deg, 13 to 29 deg, 80 to129 deg, and 10 to 21deg, respectively. In general, the ROMof the knee joint is around 60 to 115 deg for running.Figure 3(c) shows the typical knee moment-time curve in arunning cycle and Table 5 gives the moments of points E,F, G, and H from 5 studies. The ranges of points E, F, G,and H are from 1.157 to 2.574Nm/kg, -0.259 to 0.320Nm/kg,0.135 to 0.585Nm/kg, and -1.474 to -0.277Nm/kg, respec-tively. The range of moment is about 1.434 to 3.904Nm/kgfor running. Figure 3(d) shows the typical knee power-timecurve in a running cycle andTable 6 gives the powers of pointsI, J, K, and L from 6 studies. The ranges of points I, J, K, and Lare from -1.706 to -12.567W/kg, 2.739 to 9.405W/kg, -3.456to -1.525W/kg, and -3.456 to -6.732W/kg, respectively. Therange of power is about 8.724 to 21.972W/kg. This empha-sizes that the ranges of knee angle, moment, and power inrunning are far more than those in normal walking.

As shown in Figure 4(a), the stair climbing cycle (includ-ing stair ascent and descent) can be divided into two mainphases: stance phase (about 0-62% of the cycle) and swingphase (about 62-100% of the cycle) [24, 25]. The stance phaseconsists of three subphases: initial (foot contact to oppositetoe off), middle (opposite toe off to opposite foot contact),and terminal stance (opposite foot contact to toe off)[24, 26, 27]. Riener et al. [24] indicated that the knee bio-mechanics is mainly affected by the rate of leg length andstair height. Figure 4(b) shows the typical knee angle-timecurves in a stair ascent and stair descent cycle. They allinclude one peak flexion (A) and extension (B) angle. Forstair ascent, point A occurs in the swing phase and B occursin the terminal stance phase. And for stair descent, point Aoccurs in the terminal stance phase and B occurs in the swingphase. Table 7 gives the values of these points from 7 studies.The ranges of points A and B are from 83 to 102 deg and 0 to11 deg for stair ascent and from 83 to 105 deg and 1 to 19 degfor stair descent, respectively. In general, the ROM of theknee joint is around 78 to 94 deg for stair ascent and 76 to90 deg for stair descent. Figure 4(c) shows the typical kneemoment-time curves in a stair ascent and descent cycle.They all include two peak extension (E and G) and flexion(F and H) moments. For stair ascent, points E and F occurin the stance phase and G and H occur in the swing

Table 2: Overview over the experimental results of knee moment for normal walking.


meanweight ± SD(kg))Speed(m/s)

E(Nm/kg)

F(Nm/kg)

G(Nm/kg)

H(Nm/kg)

E-G(Nm/kg)

F-H(Nm/kg)

Range(Nm/kg)

Collins et al. [125] 9 (1:84 ± 0:10, 77:4 ± 9:2) 1.25 0.556 -0.245 0.207 -0.388 0.349 0.143 0.944

Shamaei et al. [3] 3 (1:76 ± 0:75, 68:6 ± 2:2) 1.25 0.335 -0.248 0.102 -0.379 0.233 0.131 0.714

Zheng [21] 1 (1.78, 70) 1.2 0.571 -0.171 0.114 0.086 0.457 -0.257 0.742

Mooney and Herr [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 0.766 -0.344 0.189 -0.378 0.577 0.034 1.144

Blazkiewicz [128] 1 (1.85, 80) — 0.263 -0.675 0.225 -0.063 0.038 -0.612 0.938

Ding et al. [132] 8 (1:76 ± 0:06, 78:5 ± 9:9) 1.25 0.777 -0.204 0.204 -0.420 0.573 0.198 1.197

Winter [133], Li et al. [134] 1 (—, 58) 1.3 0.517 -0.155 0.189 -0.224 0.328 0.069 0.741

Yang et al. [137] 1 (1.75, 70) 1.0 0.129 -0.329 0.101 -0.257 0.028 -0.072 0.458

Dijk et al. [138] 8 (1:79 ± 0:04, 75:1 ± 6:5) 1.11 0.945 0.067 0.466 -0.320 0.479 -0.387 1.265

Briggs et al. [51] 20 (1:67 ± 0:11, 58:0 ± 12:6) — 0.534 -0.276 0.190 — 0.344 — —

E: first peak knee extension moment; F: first peak knee flexion moment; G: second peak knee extension moment; H: second peak knee flexion moment.

Table 3: Overview over the experimental results of knee power for normal walking.


meanweight ± SD (kg))Speed (m/s) I (W/kg) J (W/kg) K (W/kg) L (W/kg) Range (W/kg)

Collins et al. [125] 9 (1:84 ± 0:10, 77:4 ± 9:2) 1.25 -0.571 0.286 -1.057 -1.457 1.743

Zheng [21] 1 (1.78, 70) 1.2 -0.489 0.591 -0.469 -0.321 1.080

Mooney et al. [22] 6 (1:83 ± 0:06, 89 ± 8) 1.4 -0.889 0.834 -1.334 -1.639 2.473

Malcolm et al. [16] 8 (1:67 ± 0:02, 60 ± 1) 1.38 -1.736 0.502 -0.763 -2.712 3.214

Ding et al. [132] 8 (1:76 ± 0:06, 78:5 ± 9:9) 1.25 -0.968 0.606 -1.290 -1.677 2.283

Winter [133], Li et al. [134] 1 (—, 58) 1.3 -0.755 0.324 -0.924 -1.247 1.571

Yang et al. [137] 1 (1.75, 70) 1.0 -0.116 0.296 -0.403 -0.739 1.035

Dijk et al. [138] 8 (1:79 ± 0:04, 75:1 ± 6:5) 1.1 -1.242 0.586 -1.509 -1.329 2.095

Walsh et al. [139] 1 (—, 60) 0.8 -0.828 0.667 -1.935 -1.410 2.602

I: first peak knee absorption power; J: first peak knee generation power; K: second peak knee absorption power; L: third peak knee absorption power.


phase. And for stair descent, points E, F, and G occur in thestance phase and H occurs in the swing phase. Table 8 givesthe values of these points from 7 studies. The ranges of pointsE, F, G, and H are from 0.454 to 1.409Nm/kg, -0.556

to -0.145Nm/kg, 0.027 to 0.144Nm/kg, and -0.314 to-0.121Nm/kg for stair ascent and from 0.007 to 1.512Nm/kg,-0.070 to 0.662Nm/kg, 0.365 to 1.620Nm/kg, and -0.266to 0.040Nm/kg for stair descent, respectively. In general,

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Figure 3: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for a running cycle. (a) Sketchmap of running motion [14]. (b) Knee angle-time curve ((A) first peak knee flexion angle, (B) first peak knee extension angle, (C) second peakknee flexion angle, and (D) second peak knee extension angle). (c) Knee moment-time curve ((E) first peak knee extension moment, (F) firstpeak knee flexion moment, (G) second peak knee extension moment, and (H) second peak knee flexion moment). (d) Knee power-time curve((I) first peak knee absorption power, (J) first peak knee generation power, (K) second peak knee absorption power, and (L) third peak kneeabsorption power) [23, 122, 123].

Table 4: Overview over the experimental results of knee angle for running.


meanweight ± SD (kg))Speed (m/s) A (°) B (°) C (°) D (°) C-A (°) ROM (°)

Zheng [21] 1 (1.78, 70)2.1 36 22 80 20 44 60

2.8 49 20 90 17 41 73

Hamner and Delp [23] 10 (1:77 ± 0:04, 70:9 ± 7:0)

2.0 42 18 85 11 43 74

3.0 44 16 103 12 59 91

4.0 46 15 119 13 73 106

5.0 47 15 129 14 82 115

Dollar et and Herr[122] 1 (—, 85) 3.2 43 23 89 21 46 68

Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 44 15 105 13 61 92

Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8 ± 11) 2.48 48 17 86 10 38 76

Miller et al. [141] 12 (1:66 ± 0:05, 61 ± 4:7) 3.8 60 29 96 16 36 80

Ferber et al. [52] 20 (1:81 ± 0:06, 82:3 ± 11:8) 3.65 46 13 — — — —

A: first peak knee flexion angle; B: first peak knee extension angle; C: second peak knee flexion angle; D: second peak knee extension angle.


the range of moment is about 1.010 to 1.815Nm/kg for stairascent and 0.435 to 1.815Nm/kg for stair descent. Figure 4(d)shows the typical knee power-time curves in a stair ascentand descent cycle. They all include two peak generation(I and K) and absorption (J and L) powers. For stair ascent,the whole curve lies in the generation area mostly. And forstair descent, the whole curve lies in the absorption areamostly. Table 9 gives the values of these points from 4 stud-ies. The ranges of points I, J, K, and L are from -1.044 to2.887W/kg, -0.228 to 0.071W/kg, 0.447 to 1.020W/kg, and-0.739 to -0.265W/kg for stair ascent and from -0.212 to0.569Nm/kg, -3.621 to -0.248Nm/kg, -1.326 to -0.429, and-5.485 to -2.077Nm/kg for stair descent, respectively. Ingeneral, the range of power is about 1.309 to 3.481W/kg forstair ascent and 2.114 to 6.054W/kg for stair descent.

As shown in Figure 5(a), the sit-to-stand begins in a sitposture and ends in a stand posture. Figures 5(b)–5(d) showthe typical knee angle-time, moment-time, and power-timecurves in sit-to-stand cycle, respectively. For the knee joint,there are only extension angle, extension moment, andgeneration power in the whole sit-to-stand movement. Themaximum angle, moment, and power occur in nearly thesame time that the buttocks leave the chair. Hurley et al.[28] represented that the biomechanics of knee joint ismainly affected by the rate of leg length and chair height.Table 10 gives the experimental results of knee angle from

6 studies. The ranges of points A and B are from 82 to96 deg and -3 to 22 deg, respectively. In general, the ROMof the knee joint is around 60 to 87 deg for sit-to-stand cycle.Table 11 gives the experimental results of knee moment from9 studies. The ranges of points E and F are from 0.619 to2.187Nm/kg and -0.198 to 0.609Nm/kg, respectively. In gen-eral, the range of moment is about 0.619 to 1.578Nm/kg forsit-to-stand cycle. The researchers about knee power in sit-to-stand is rare, and only two researchers have been found.Spyropoulos et al. [29] reported that the knee power wasabout 1.973W/kg for sit-to-stand. But Kamali et al. [30]pointed out that the value was about 0.560W/kg forsit-to-stand.

Because of the complicated interaction of the underlyingbiological mechanisms, the knee joint demonstrates a spring-like behavior in common motions [31–33]. Figure 6 showsthe typical knee moment-angle curves in the sagittal plane.A linear relationship can be seen during the sit-to-stand,and the weight acceptance and swing phase of walking, run-ning, and stair climbing. Quasistiffness refers to the slope ofthe linear fit to the knee moment-angle curve [33]. Duringwalking, running, and stair climbing, a high stiffness in theweight acceptance phase and a low stiffness in the swingphase can be observed. For walking, Zhu et al. [20] andWang[12] found that the knee quasistiffness was around 3.0 and2.27Nm/deg in the stand phase. Sridar et al. [34] indicated

Table 5: Overview over the experimental results of knee moment for running.


meanweight ± SD (kg))Speed(m/s)

E(Nm/kg)

F(Nm/kg)

G(Nm/kg)

H(Nm/kg)

E-G(Nm/kg)

F-H(Nm/kg)

Range(Nm/kg)

Zheng [21] 1 (1.78, 70)2.1 1.157 -0.030 0.274 -0.277 0.883 0.247 1.434

2.8 1.749 0.320 0.320 -0.351 1.429 0.671 2.100

Hamner and Delp [23] 10 (1:77 ± 0:04, 70:9 ± 7:0)

2.0 1.798 -0.205 0.135 -0.697 1.663 0.492 2.495

3.0 2.159 -0.226 0.269 -0.925 1.890 0.699 3.084

4.0 2.402 -0.233 0.405 -1.147 1.997 0.914 3.549

5.0 2.430 -0.259 0.585 -1.474 1.845 1.215 3.904

Dollar and Herr [122] 1 (—, 85) 3.2 1.571 0.175 0.175 -0.591 1.396 0.766 2.162

Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 2.196 -0.249 0.248 -0.775 1.948 0.526 2.971

Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8 ± 11) 2.48 2.574 -0.221 0.307 -0.649 2.267 0.428 3.223

E: first peak knee extension moment; F: first peak knee flexion moment; G: second peak knee extension moment; H: second peak knee flexion moment.

Table 6: Overview over the experimental results of knee power for running.


meanweight ± SD (kg))Speed (m/s) I (W/kg) J (W/kg) K (W/kg) L (W/kg) Range (W/kg)

Zheng [21] 1 (1.78, 70)2.1 -5.859 4.336 -2.231 -3.521 10.195

2.8 -8.008 7.386 -3.456 -3.456 15.394

Dollar and Herr [122] 1 (—, 85) 3.2 -1.706 4.766 -1.525 -3.958 8.724

Elliott [123] 6 (1:81 ± 0:08, 69 ± 11) 3.5 -9.013 4.539 -2.439 -6.732 13.552

Sobhani et al. [140] 16 (1:77 ± 0:09, 69:8 ± 11) 2.48 -12.567 9.405 -2.371 -4.473 21.972

Ferber et al. [52] 20 (1:81 ± 0:06, 82:3 ± 11:8) 3.65 -5.462 2.739 — — —

Heiderscheit et al. [62] 45 (1:76 ± 0:10, 69:5 ± 13:1) 2.9 -6.948 5.422 — — —

I: first peak knee absorption power; J: first peak knee generation power; K: second peak knee absorption power; L: third peak knee absorption power.


Stance (62%)

0%

Initial Middle Terminal

20% 40% 60% 80% 100%

Swing (38%)

(a)

100

80

60

A A

BB

40

Knee

angl

e (de

g)

20 Flex

ion

0


Ascent

Descent

(b)

E

EG

G

HHF

F

Ascent

Descent

Knee

mom

ent (

Nm

)

Exte

nsio

n

120

60

0

–600% 20% 40% 60% 80% 100%


(c)

Ascent

Descent

JJ

K

K

L

L

I

I

Knee

pow

er (W

)

Gen

erat

ion

300

150

–150

–300

0


(d)

Figure 4: A sketch map of motion and the typical curves of knee angle, moment, and power in sagittal plane for stair ascent and stair descent.(a) Sketch map of the stair ascent and stair descent motion. (b) Knee angle-time curve ((A) peak knee flexion angle and (B) peak kneeextension angle. (c) Knee moment-time curve ((E) first peak knee extension moment, (F) first peak knee flexion moment, (G) second peakknee extension moment, and (H) second peak knee flexion moment). (d) Knee power-time curve ((I) first peak knee generationpower, (J) first peak knee absorption power, (K) second peak knee generation power, and (L) second peak knee absorption power) [24, 25].

Table 7: Overview over the experimental results of knee angle for stair ascent and stair descent.


meanweight ± SD (kg))Riser × tread (cm× cm) Type A (°) B (°) ROM (°)

Riener et al. [24], Joudzadeh et al. [25] 10 (1:79 ± 0:05, 82:2 ± 8:5)

13:8 × 31:0 Ascent 91 9 82

Descent 89 13 76

17:0 × 29:0 Ascent 95 9 86

Descent 93 15 78

22:5 × 25:0 Ascent 102 10 92

Descent 102 13 89

Mcfadyen and Winter [142] 3 (—, —) 22:0 × 28:0 Ascent 99 11 88

Descent 105 19 86

Zhang et al. [143] 10 (1:74 ± 0:05, 72:7 ± 8:6) 18:0 × 28:0 Ascent 89 7 82

Descent 96 10 86

Musselman [27] 17 (1:85 ± 0:12, 82 ± 14) 15:0 × 26:0 Ascent 83 5 78

Descent 83 6 77

Protopapadaki et al. [144] 33 (1:69 ± 0:08, 67:5 ± 12:1) 18:0 × 28:5 Ascent 94 0 94

Descent 91 1 90

Law [26] 19 (1:64 ± 0:08, 59:5 ± 7:8) 17:0 × 28:0 Ascent 95 11 84

Descent 93 3 90

A: peak knee flexion angle; B: peak knee extension angle.


Table8:Overviewover

theexperimentalresultsof

knee

mom

entforstairascent

andstairdescent.

Stud

ySubjects(m

eanh

eight

±SD

(m),

meanw

eight

±SD

(kg))

Riser×

tread

(cm

×cm

)Type

E(N

m/kg)

F(N

m/kg)

G(N

m/kg)

H(N

m/kg)

E-G

(Nm/kg)

F-H

(Nm/kg)

Range

(Nm/kg)

Rieneretal.[24]andJoud

zadeh

etal.[25]

10(1:79±

0:05,82:2±

8:5)

13:8×31:0

Ascent

1.055

-0.179

0.027

-0.183

1.028

0.004

1.238

Descent

0.916

0.587

1.247

-0.096

-0.331

0.683

1.343

17:0×29:0

Ascent

1.093

-0.218

0.042

-0.177

1.051

-0.041

1.311

Descent

1.006

0.662

1.345

-0.091

-0.339

0.753

1.436

22:5×25:0

Ascent

1.164

-0.247

0.037

-0.172

1.127

0.075

1.411

Descent

0.991

0.653

1.470

-0.088

-0.479

0.741

1.558

McfadyenandWinter[142]

3(—

,—)

22:0×28:0

Ascent

1.409

-0.406

0.164

-0.314

1.245

-0.092

1.815

Descent

1.512

0.405

1.620

-0.266

-0.108

0.671

1.886

Zhang

etal.[143]

10(1:74±

0:05,72:7±

8:6)

18:0×28:0

Ascent

0.588

-0.493

0.144

-0.256

0.444

-0.237

1.081

Descent

0.338

0.152

1.106

-0.201

-0.768

0.353

1.307

Musselm

an[27]

17(1:85±

0:12,82±

14)

15:0×26:0

Ascent

0.921

-0.456

0.043

-0.206

0.878

-0.250

1.377

Descent

0.448

0.263

1.012

-0.167

-0.564

0.430

1.179

Protopapadaki

etal.[144]

33(1:69±

0:08,67:5±

12:1)

18:0×28:5

Ascent

0.454

-0.556

0.032

-0.121

0.422

-0.435

1.010

Descent

0.007

-0.070

0.365

-0.040

-0.358

-0.030

0.435

Law[26]

19(1:64±

0:08,59:5±

7:8)

17:0×28:0

Ascent

0.899

-0.145

0.046

-0.147

0.085

0.002

1.036

Descent

0.603

0.439

1.006

-0.076

-0.403

0.515

1.082

E:fi

rstpeak

knee

extensionmom

ent;F:

firstpeak

knee

flexionmom

ent;G:secon

dpeak

knee

extensionmom

ent;H:secon

dpeak

knee

flexionmom

ent.


that the knee quasistiffness was around 1.07Nm/deg in theswing phase. For running, Elliott et al. [35, 36] found thatthe knee quasistiffness was around 0.38Nm/deg in the swingphase and 6.6Nm/deg in the stand phase. For stair climbing,Riener et al. [24] reported that the knee quasistiffness wasaround 2.37Nm/deg and 2.42Nm/deg in the weight accep-tance phase of stair ascent and stair descent and 0.19Nm/deg

and 0.04Nm/deg in the swing phase of stair ascent and stairdescent, respectively. For sit-to-stand, Wu et al. [37] reportedthat the knee quasistiffness was around 1.1Nm/deg.

3.1.2. The Real Motion and Coronal Plane Biomechanics ofKnee Joint. Since the nonuniform shape of the knee articularsurface and the complicated physical structure of the femur

Table 9: Overview over the experimental results of knee power for stair ascent and stair descent.


meanweight ± SD (kg))Riser × tread(cm × cm)

TypeI

(W/kg)J

(W/kg)K

(W/kg)L

(W/kg)Range(W/kg0

Riener et al. [24] andJoudzadeh et al. [25]

10 (1:79 ± 0:05, 82:2 ± 8:5)

13:8 × 31:0 Ascent 2.322 0.071 0.647 -0.309 2.631

Descent 0.256 -0.678 -0.429 -3.788 4.044

17:0 × 29:0 Ascent 2.538 0.055 0.696 -0.312 2.850

Descent 0.305 -1.029 -0.453 -4.141 4.446

22:5 × 25:0 Ascent 2.887 0.049 0.811 -0.288 3.175

Descent -0.212 -1.255 -0.472 -4.843 4.631

Mcfadyen and Winter [142] 3 (—, —) 22:0 × 28:0 Ascent 2.742 -0.228 1.020 -0.739 3.481

Descent 0.569 -3.621 -1.326 -5.485 6.054

Musselman [27] 17 (1:85 ± 0:12, 82 ± 14) 15:0 × 26:0 Ascent 1.044 -0.223 0.447 -0.265 1.309

Descent 0.037 -0.248 -0.558 -2.077 2.114

I: first peak knee generation power; J: first peak knee absorption power; K: second peak knee generation power; L: second peak knee absorption power.

0% 20% 40% 60% 80% 100%

(a)

100

80

60

A

B

40

Knee

angl

e (de

g)

20 Flex

ion

0

0% 20% 40% 60% 80% 100%Time (% sit-to-stand completion)

(b)

Time (% sit-to-stand completion)

E

F

Knee

mom

ent (

Nm

)

Exte

nsio

n

120

60

0

–600% 20% 40% 60% 80% 100%

(c)

Time (% sit-to-stand completion)

I

Knee

pow

er (W

)

Gen

erat

ion

300

150

–150

–300

0

0% 20% 40% 60% 80% 100%

(d)

Figure 5: A sketch map of motion and the typical curves of knee angle, moment, and power in the sagittal plane for sit-to-stand. (a) Sketchmap of sit-to-stand cycle [28]. (b) Knee angle-time curve ((A) peak knee flexion angle and (B) peak knee extension angle). (c) Knee moment-time curve ((E) peak knee extension moment and (F) peak knee flexion moment). (d) knee power-time curve ((I) peak knee generationpower) [37, 124].


and tibia, the knee motion cannot be modeled as simple as aperfect hinge [38–40]. The real knee joint moves with a poly-centric motion, whereby the center of rotation changes dur-ing the rotation [41]. The femur and tibia can beapproximated as a bielliptical structure, so the tibia rolls onthe femur resulting in anterior-posterior (A-P) translationduring the flexion-extension motion [40]. When the rotationangle is less than 20deg, there would be a small A-P transla-tion. Thus, the movement of a real knee joint can be approx-imated as pure rolling around the fixed center. But when therotation angle is more than 20deg, the A-P translation beginsto increase, the amplitude of which can exceed 19mm. Thus,the knee motion can be approximated as a gradual transitionfrom pure rolling, the coupled motion of rolling, and slidingto pure sliding [38, 40, 42]. Smidt [43] reported that the tra-jectory of the center of knee seems to be a J-shaped curve inthe sagittal plane.

In addition to the motion in the sagittal plane, the kneejoint also has internal-external rotation in the horizontalplane [44]. During the last 10-15 deg before complete exten-sion, the medial femoral condyle is internally rotated and thetibia is externally rotated. At the same time, the lateral menis-cus is anteriorly translated and the medial meniscus is poste-riorly translated. Because of the larger contact surface of themedial tibiofemoral joint, the length of the medial femoralcondyle is longer than that of the lateral, and because of thelimitations of cruciate-collateral ligaments and quadricepsfemoris on knee motion, the knee joint is self-locking as aneccentric wheel to maintain the stability of the joint during

the knee extension motion [44, 45]. Blankevoort et al. [46],Churchill et al. [47], and Hollister et al. [48] found that theflexion-extension and internal-external rotation cause thetrajectory of the knee center seem to be a spiral curve.

In the coronal plane, the knee adduction moment and theloads of knee medial and lateral compartments are keyparameters of biomechanics. For the former, Gaasbeek et al.[49], Russell [50], and Briggs et al. [51] found that the maxi-mum adduction moment is about 0.31, 0.36, and0.26Nm/(kg⋅m) in walking, respectively. Ferber et al. [52],Sinclair [53], and Gehring et al. [54] reported that the maxi-mum adduction moment is about 0.52, 0.53, and0.58Nm/(kg⋅m) in running, respectively. Law [26] and Mus-selman [27] represented that the maximum adductionmoment is about 0.44 and 0.34Nm/kg in stair climbing,respectively. Trepczynski et al. [55] reported that the maxi-mum adduction moment is about 0.45Nm/kg in sit-to-stand. For the latter, Russell [50] found that the normal kneejoint always had a little varus, in other words, the medialcompartment bears more load than the lateral compartment.Specogna et al. [56] reported that the weight-bearing line(WBL) was different in each phase of the gait. Cao [57]reported that the medial compartment bears 60-80% of theload. Pagani et al. [58] found that about 70% joint force passthrough the medial compartment to the ground.

3.2. Biomechanical Properties of Diseased Knee Joint. Accord-ing to the pathogeny, the knee disorders can be mainlydivided into musculoskeletal and neurological disorders.

Table 10: Overview over the experimental results of knee angle for sit-to-stand.


meanweight ± SD (kg))A (°) B (°) ROM (°)

Wu et al. [37] 1 (—, 75) 96 9 87

Hurley et al. [28] 10 (1:77 ± 0:08, 77 ± 13) 90 12 78

Spyropoulos et al. [29] 17 (1:65 ± 0:07, 54:6 ± 5) 86 -1 87

Karavas et al. [124] 1 (1.85, 82.5) 86 5 81

Yu et al. [145] 10 (1:65 ± 0:05, 46:2 ± 0:8) 82 22 60

Bowser et al. [146] 12 (1:66 ± 0:08, 74:2 ± 19:5) 83 -3 86

A: peak knee flexion angle; B: peak knee extension angle.

Table 11: Overview over the experimental results of knee moment for running.


meanweight ± SD (kg))E (Nm/kg) F (Nm/kg) Range (Nm/kg)

Wu et al. [37] 1 (—, 75) 2.187 0.609 1.578

Hurley et al. [28] 10 (1:77 ± 0:08, 77 ± 13) 0.619 0 0.619

Yoshioka et al. [147] 1 (—, 73.8) 1.087 -0.038 1.125

Spyropoulos et al. [29] 17 (1:65 ± 0:07, 54:6 ± 5) 1.132 -0.157 1.289

Karavas et al. [124] 1 (1.85, 82.5) 1.293 0.168 1.125

Bowser et al. [146] 12 (1:66 ± 0:08, 74:2 ± 19:5) 0.901 0 0.901

Kamali et al. [30] 1 (1.72, 70) 1.126 0.136 0.990

Schofield et al. [148] 10 (1:77 ± 0:09, 70:5 ± 8:7) 0.679 0.038 0.641

Robert et al. [149] 7 (1:75 ± 0:06, 66 ± 8) 1.136 -0.198 1.334

E: peak knee extension moment; F: peak knee flexion moment.


For the former, the pathogeny is inside the knee joint, but theneural control system of these patients is normal. Knee oste-oarthritis (KOA), knee ligament injury, and meniscus injuryare the most common forms of these disorders and will bemainly discussed in this section. Some evidences showed thatthe partial assistance from an external mechanism can allevi-ate the symptoms [59]. For the latter, the actuator of the kneeis normal, but the knee control system or more advancedcontrol system is injured. Although it is not considered aknee joint disease in the medical field, the neurological disor-ders can influence the knee movement biomechanics. Spinalcord injury (SCI), stroke, and cerebral palsy (CP) are themost common forms of these disorders and will be mainlydiscussed in this section. Some researchers pointed out thatthe partial or entire assistance from an external mechanismand rehabilitation training can recover the ambulatory abilityof this patients [60, 61].

3.2.1. Knee Musculoskeletal Disorders and Its BiomechanicalEffects. KOA, one of the major health problems, affects7-17% of individuals especially for the elder, obese, andprevious limb injury people [62–65]. Nearly 46% of adultswill develop painful KOA in at least one knee joint over theirlifetime [66]. By 2020, the KOA is predicted to become thefourth leading cause of disability globally [67]. The etiologyand progression of KOA are multifactorial, which includesthe increasing tibiofemoral force, the femoral shaft curvature

changes, enlarging bone marrow lesions, compartment carti-lage loss, joint space narrowing, and tibial plateau compres-sion. [63, 68]. From the biomechanical view, these causeswill change the tibiofemoral alignment and influence the loaddistribution, and then result in the deterioration of KOA[69]. Due to the medial compartment bearing about 70% ofthe total force, KOA is more commonly observed in themedial compartment (MKOA) than the lateral compartmentwith a ratio of up to 4 times [58, 59].

Medical radiological assessment, kinematics analysis,kinetics analysis, and knee muscle analysis are the commonbiomechanical methods for KOA, as shown in Table 12. Inthe medical radiological assessment aspect, the hip-knee-ankle angle (HKAA) on the full-0limb radiograph is regardedas the gold standard of alignment measurement, as shown inFigure 7(a) [63, 69]. Chao et al. [70] reported that the normalHKAAwas about 178.8 deg and the angle is less than the valuerepresented by genu varum. Russell [50] found that theHKAA of normal and MKOA were about 177.7 deg and174.2 deg, respectively. As shown in Figure 7(a), mechani-cal-lateral-distal-femoral angle (mLDFA), medial-proximal-tibial angle (MPTA), and joint-line-convergence angle(JLCA) are also commonly used as the measurement param-eters [68]. The normal values of these angles are 85-90 deg,85-90 deg, and 0-2 deg, respectively. ThemLDFA greater than90 deg, MPTA less than 85 deg, or JLCA greater than 2degrepresent genu varum [71]. The mechanical axis deviation

Knee

mom

ent (

Nm

)

Exte

nsio

n

Flexion

120

60

Stance

SwingHeelstrike

0

–600 20 40 60 80 100

Knee angle (deg)

(a)

Stance

SwingHeelstrike

Knee

mom

ent (

Nm

)

Exte

nsio

n

Flexion

120

60

0

–600 20 40 60 80 100

Knee angle (deg)

(b)

Knee

mom

ent (

Nm

)

Exte

nsio

n

Flexion

120

60

0

–600 20 40 60 80 100

Knee angle (deg)

Descent

Ascent

(c)

Stand SitKnee

mom

ent (

Nm

)

Exte

nsio

n

Flexion

120

60

0

–600 20 40 60 80 100

Knee angle (deg)

(d)

Figure 6: The moment-angle (stiffness) curves of the knee joint for normal walking, running, stair climbing, and sit-to-stand. (a) Normalwalking [20, 34]. (b) Running [35, 36]. (c) Stair ascent and stair descent [24]. (d) Sit-to-stand [37].


(MAD) is another measurement method. The normal MADis about 8mm in the medial, and the value greater than thenormal MAD represents genu varum [71]. Besides, the WBLratio andmedial or lateral joint space also used to characterizethe KOA. Russell [50] pointed out that theWBL ratio, medialjoint space, and lateral joint space were about 41.4%, 4.5mm,and 5.5mm for normal individuals and 24.2%, 2.8mm and7.9mm for MKOA, respectively. In the knee kinematicsaspect, Russell [50] reported that the knee flexion patternwas similar, but the magnitude was lower for MKOA patientscompared to that for normal subjects, as shown in Figure 7(b).

Zhu et al. [72] found that the KOApatients presented a longergait time, a smaller stride length and ROM, a greater kneeflexion angle at heel strike, and an unobvious fluctuation ofknee flexion angle in the stand phase of walking. Alzahrani[73] indicated that the MKOA patients presented slowerwalking speeds, shorter step lengths, longer stance and doublesupport time, and smaller cadence, stride length, and kneeROM. In the knee kinetics aspect, Russell [50] described thatthe knee adductionmoment pattern was similar, but themag-nitude was higher for MKOA patients compared to that fornormal subjects in walking, as shown in Figure 7(c).

Table 12: Overview over the biomechanical effects of KOA.

Study Analysis Effects

Chao et al. [70] Medical radiology HKAA: ~178.8 deg for normal knee; <178 deg for MKOA patients

Paley [71] Medical radiology

mLDFA: 85-90 deg for normal knee; >90 deg for MKOA patientsMPTA: 85-90 deg for normal knee; <85 deg for MKOA patientsJLCA: 0-2 deg for normal knee; >2 deg for MKOA patientsMAD: ~8mm for normal knee; >8mm for MKOA patients

Russell [50]

Medical radiology

HKAA: ~177.7 deg for normal knee; ~174.2 deg for MKOA patientsWBL ratio: ~41.4% for normal knee; ~24.2% for MKOA patients

Medial joint apace: ~4.5mm for normal knee; ~2.8mm forMKOA patients

Lateral joint apace: ~5.5mm for normal knee; ~7.9mm forMKOA patients

Kinematics A lower knee flexion angle for MKOA patients

Kinetics A higher knee adduction moment for MKOA patients

Muscles A lower quadriceps strength for MKOA patients

Zhu et al. [72] KinematicsA longer gait time, a smaller stride length and ROM, a greater kneeflexion angle at heel strike, and an unobvious fluctuation of knee

flexion angle in stand phase of walking for MKOA patients

Alzahrani [73]Kinematics

A slower walking speed, a shorter step length, a longer stance, anddouble support time, and smaller cadence, stride length, and knee

ROM for MKOA patients

MusclesThe medial and lateral muscle cocontraction was increased for KOA

patients

Astephen et al. [74] Kinetics A greater knee adduction moment in mid-stance for MKOA patients

Guo et al. [75] KineticsA greater peak adduction moment during stair climbing for MKOA

patients

Rudolph et al. [76] and Schmittand Rudolph [77]

KineticsA smaller peak knee flexion moment during early and late stance

phases for MKOA patients

Fitzgerald [78] KineticsA 4-6 deg increase in varus alignment could increase around 70-90%

medial compartment load during single limb bearing

Lim et al. [79]Kinetics

Genu varum exceeding 5 deg was associated with greater functionaldeterioration over 18 months than the value of 5 deg or less

MusclesNo significant relationship between the varus malalignment and the

EMG ratio of VM and VL

Kemp et al. [80] KineticsA 20% increase in the peak adductionmoment could increase the KOA

progression risk

Slemenda et al. [81], Hurley et al.[82], and Oreilly et al. [83]

Muscles A smaller quadriceps strength and muscle activation for KOA patients

Hubley-Kozey et al. [84] MusclesThe medial and lateral muscle cocontraction was increased for KOA

patients


Astephen et al. [74] observed that the knee adductionmoment in MKOA patients was greater than that in the nor-mal in mid-stance. Guo et al. [75] found that the MKOApatients possessed a greater peak adduction moment duringstair climbing. Rudolph et al. [76] and Schmitt and Rudolph[77] pointed out that the peak knee flexion moment in KOApatients was smaller than that in the normal during earlyand late stance phases. Fitzgerald et al. [78] reported that a4-6 deg increase in varus alignment could increase around70-90% medial compartment load during single limb bear-ing. Lim et al. [79] indicated that genu varum exceeding5 deg at baseline was associated with greater functional dete-rioration over 18 months than the value of 5 deg or less.Kemp et al. [80] observed that a 20% increase in the peakadduction moment could increase the KOA progression risk.In the knee muscle aspect, Slemenda et al. [81], Hurley et al.[82], and Oreilly et al. [83] found that the KOA patients hadsmaller quadriceps strength and muscle activation. Lim et al.[79] indicated that there was no significant relationshipbetween the varus malalignment and the EMG ratio ofVM and VL. Russell [50] reported that the medial muscle(VM-ST and VM-MG) and lateral muscle (VL-BF andVL-LG) cocontraction indices were not significantly differentbetween MKOA patients and normal person, but the quadri-ceps strength was significantly lower for MKOA patients.Alzahrani [73] and Hubley-Kozey et al. [84] represented thatthe medial and lateral muscle cocontraction was increasedfor the KOA patients.

Knee ligament injury is a common and serious disease insport injuries and can significantly change the biomechanics.According to where the injury hits, the knee ligament injurycan be divided into the ACL, PCL, TCL, FCL, and PLinjuries. Many researchers pointed out that the secondaryinjuries, e.g., cartilage injury, meniscus injury, and KOA,can occur if not treated in time. And the ligament recon-struction, as a recognized effective treatment, can dramati-cally recover the knee biomechanics [85–88]. In the fivetypes of injures, nearly half of ligament injuries are isolated

injuries to the ACL [89]. So, ACL injury will be mainly dis-cussed in this section.

The biomechanical effects of ACL were shown inTable 13. In the knee kinematics aspect, Zhao et al. [90]reported that the knee ROM was lower for ACL-injuredpatients in stair climbing. Slater et al. [91] pointed out thatthe peak knee flexion angle was smaller and the peak kneeadduction angle was greater for the ACL injury patients inwalking. Cronstrom et al. [92] represented that the kneeadduction degree during weight-bearing activities for ACL-injured patients was greater in walking. Gao and Zheng[93] indicated that the ACL-injured patients had slowerspeed and smaller stride length during walking. In the kneekinetics aspect, Alexander and Schwameder [94] observed a430% and 475% increase in the patella-femur contact forcefor ACL-injured patients during upslope and downslope,respectively. Goerger et al. [95] found that the peak kneeadduction moment during weight-bearing activities wasgreater in patients after ACL than before injury. Slater et al.[91] reported that a smaller peak external knee flexion andadduction moment can be found in the ACL-injured patientsduring walking. Thomas and Palmieri-Smith [96] illustratedno difference in the external knee adduction moment amongindividuals with ACL injury and those who are healthy. Nor-cross et al. [85] demonstrated that the ACL-injured patientshad a greater knee energy adsorption during landing.

Meniscus injury, as a sport-induced injury, is com-mon among athletes and general population [86, 89].The meniscus-injured patients are often coupled with trau-matic ACL injury and can increase the stress and reducethe stability of the knee joint during extension and flexionmotions [89]. Many studies described that the secondarydiseases, e.g., cartilage wear and KOA, can occur if nottreated in time [87, 88, 97]. According to the injured degree,different treatments including conservative treatment, menis-cus suture, and meniscectomy, can be selected.

To our knowledge, there are rare research that study thebiomechanical effects of meniscus injury, as shown in

mLDFAHKAA

MPTA

MAD

(a)

60

40

Knee

flex

ion

angl

e (de

g)

20

00 20 40 60

Time (% stance)80 100

HealthKOA

(b)

0.4

0.3

0.2

0.1

0.0

Knee

addu

ctio

n m

omen

t (N

m/k

g·m

)

0Time (% stance)

20 40 60 80 100

HealthKOA

(c)

Figure 7: The knee alignment measurement methods and the effect of KOA on flexion angle and adduction moment. (a) Sketch map ofHKAA, mLDFA, MPTA, and MAD [61]. (b) Knee flexion angles of health and KOA individuals [48]. (c) Knee adduction moments ofhealth and KOA subjects [48].


Table 13. Magyar et al. [87] represented that the walkingspeed and knee ROM of meniscus-injured patients were sig-nificantly smaller, and the cadence, step length, duration ofsupport, and double support phase of meniscus-injuredpatients were remarkably larger in walking. Zhou [86] indi-cated that the maximum flexion angle and maximumabduction-adduction angle between meniscus injury patientsand healthy subjects have no apparent difference. Themeniscus-injured patients had a larger minimum flexionangle and a smaller maximum internal-external rotationangles in walking. And the knee stressed area was smallerand the knee pressure was larger for the meniscus-injuredpatients in walking.

3.2.2. Knee Neurological Disorders and Its BiomechanicalEffects. SCI, one of the main causes of mobility disorders,affects around 0.25-0.5 million people every year aroundthe world especially the young [98]. Approximately 43% ofSCI patients turn out to have paraplegia and the number isincreasing year by year [99]. The SCI patients are at anincreasing risk of many secondary medical complications,including muscle atrophy, pressure ulcer, bone densityreduction, and osteoporosis [100, 101]. Standing and walk-ing, as the most prevalent desires of these patients, can stim-ulate blood circulation, ease muscle spasm, and increase thebone mineral density [98, 102]. Some evidences showed thatthe SCI patients can reduce the secondary medical complica-tions risk and recover motion capabilities by standing or

walking for several hours per day [98, 99, 102, 103]. The bio-mechanical effects of SCI were shown in Table 14. Barbeauet al. [104] pointed out that the knee ROM and peak knee-swing-flexion angle were lower, and peak knee moment waslarger for SCI patients in walking. Desrosiers et al. [105]found that the knee power was lower for SCI patients inuphill and downhill walking. Pepin et al. [106] indicated thatthe SCI patients presented a longer flexed knee at good con-tact and maintain the longer flexion throughout the stancephase of walking.

Stroke, a common cerebrovascular disease, has a highmortality and disability rate [107, 108]. There are about 7.0million stroke survivals in China and 6.6 million in theUnited States [109, 110]. Stroke is known as the cause ofparalysis, loss of motor function, paresis-weakness of muscle,plegia-complete loss of muscle action, and muscle atrophy[34, 108, 109]. Impaired walking and sit-stand transitionare the main reason that poststroke patients cannot live inde-pendently [107, 108]. And about 30% of poststroke patientshave difficulty in ambulation without assistance [109]. Someevidences showed that 70% of poststroke patients can recovertheir walking capabilities by rehabilitation [108, 111]. Thebiomechanical effects of stroke were shown in Table 14.Sridar et al. [109] indicated that the kinematic and kineticperformance of the poststroke patients will degrade, such asreduced walking speed, quadriceps muscle moment, andquadriceps muscle power. Chen et al. [112] revealed thatthe poststroke patients had lower knee flexion in the swingphase of walking. Stanhope et al. [113] found that the

Table 13: Overview over the biomechanical effects of ACL and meniscus injury.

Study Knee disorders Analysis Effects

Zhao et al. [90] ACL Kinematics A lower knee ROM during stair climbing for ACL-injured patients

Gronstrom et al. [92] ACL KinematicsA greater knee adduction angle during weight-bearing activities for

ACL-injured patients

Gao and Zheng[93] ACL KinematicsA slower speed and smaller stride length during walking for

ACL-injured patients

Alexander and Schwameder[94] ACL KineticsA 430% and 475% increase in the patella-femur contact force during

upslope and downslope, respectively, for ACL-injured patients.

Goerger et al. [95] ACL KineticsA greater peak knee adduction moment during weight-bearing

activities for ACL-injured patients

Slater et al. [91] ACLKinematics

A smaller peak knee flexion angle and a greater peak knee adductionangle during walking for ACL-injured patients

Kinetics A smaller peak E-KFM and E-KAM for ACL-injured patients

Thomas et al. [96] ACL KineticsNo difference in the E-KAM among individuals with ACL injury and

those who are healthy

Norcross et al. [85] ACL Kinetics A greater knee energy adsorption for ACL-injured patients

Magyar et al. [87] Meniscus injury KinematicsA smaller walking speed and knee ROM and a larger cadence, steplength, duration of support, and double support phase for meniscus

injured patients

Zhou [86] Meniscus injuryKinematics

A larger minimum flexion angle and a smaller maximuminternal-external rotation angle for meniscus-injured patients

KineticsA larger knee pressure and a smaller knee stressed area for

meniscus-injured patients


poststroke patients can compensate their poor knee flexion inwalking through faster speed. Marrocco et al. [114] reporteda greater dynamic medical knee joint loading in stroke sub-jects in walking. However, the external knee adduction andflexion moments in walking were not significantly differentbetween the stroke patients and healthy subjects. Novaket al. [115] observed that less energy was transferred concen-trically via knee extensor muscles of stroke patients in mid-stance of walking. And the stroke patients presented lowerenergy absorption by the knee extensors in the late stanceof walking.

CP, the most common pediatric neuromotor disorder,affects around 0.2-0.3% live births [19, 116]. The injury inthe central nervous system of the developing fetus or infantis the pathogenesis of CP, which effects the control of move-ment, balance, and posture [116, 117]. The person with CPalways has a variety of characteristics including rigidity, spas-ticity, abnormal aerobic and anaerobic capacity, decreasedmuscle strength and endurance, abnormal muscle tone,deformities, and muscle weakness [19, 118, 119]. The biome-chanical effects of CP were shown in Table 14. Crouch gait,characterized by excessive knee flexion in stance phase, is afrequent gait deviation in CP patients [19, 117, 118]. Hickset al. [120] reported the minimum knee flexion angle duringthe stance phase exceed 40 deg for the CP patients. Com-pared with the normal gait, crouch gait is inefficient andconsumes much more energy [19, 116]. For maintainingthe excessive knee flexion posture in walking, the stress ofthe knee and surrounding muscles are increasing, whichcan lead to bony deformities, degenerative arthritis, joint

pain, and patellar stress fractures and then result in theseverity of crouch gait [19, 118, 121]. Some evidencesshowed that the mobility function can be preserved andthe complications can be reduced by limiting excessive kneeflexion in walking [118].

4. Discussion and Conclusions

Knee disorders, including musculoskeletal and neurologicaldisorders, have serious influences on knee biomechanics. Anumber of researches related with the biomechanics of nor-mal and diseased knee joint have been done during the lastdecades. Many advances have been made to understand thekinematics and kinetics of normal and diseased knee duringdifferent common motions. In the aspect of normal knee bio-mechanics, there is no clear assessment at the current state-of-the-art. The difference between the results of differentresearches is significant. In the aspect of diseased knee bio-mechanics, a lower knee flexion angle, walking speed, mus-cles strength, and a higher knee contact pressure werealways observed. Understanding how pathologies affect theknee joint biomechanics is important for designing kneeassistive devices and optimizing rehabilitation exercise pro-gram. However, the current understanding still has not metthe requirement of a designer and rehabilitative physician.And it is hard to find a research that can systematic studyall aspects of knee biomechanics completely. Thus, deeperunderstanding of the biomechanics of normal and diseasedknee joint will still be an urgent need in the future.

Table 14: Overview over the biomechanical effects of SCI, stroke, and CP.

Study Knee disorders Analysis Effects

Barbeau et al. [102] SCIKinematics A lower knee ROM and peak knee-swing-flexion angle for SCI patients

Kinetics A larger peak knee moment for SCI patients

Desrosiers et al. [103] SCI KineticsA lower knee power during uphill and downhill walking for SCI

patients

Pepin et al. [104] SCI KinematicsA longer knee flexion at good contact and maintain the longer flexion

throughout the stance phase of walking for SCI patients.

Sridar et al. [109] StrokeKinematics A lower walking speed for stroke patients

Muscles A lower quadriceps muscle moment and power for stroke patients

Chen et al. [112] Stroke KinematicsA lower knee flexion in the swing phase of walking for poststroke

patients

Stanhope et al. [113] Stroke KinematicsPost-stroke patients can compensate their poor knee flexion in walking

through faster speed

Marrocco et al. [114] Stroke KineticsA greater dynamic knee joint loading for stroke patients and nosignificant difference between the E-KFM/E-KAM of stroke and

healthy subjects.

Novak et al. [115] Stroke KineticsA less energy transference in mid-stance of walking and a lower energy

absorption in the late stance of walking for stroke patients

Lerner [19] and Thapa et al. [116] CP KineticsCrouch gait (characterized by excessive knee flexion in stance phase),

walking inefficiency, and consumes much more energy

Hicks et al. [120] CP KinematicsMinimum knee flexion angle during the stance phase exceeding 40 deg

for CP patients


Some limitations of the current studies must be noted.First, the current understanding on the knee biomechanicsis not enough. Many research about the theoretical analysisof knee biomechanics are based on the mathematical model-ing. Whether a link model or a simulation model, there is adifference between the model and the reality. And somesimplification should always be made, such as the mechani-cal property, geometry, and relative motion of the bone,muscle, cartilage, etc. Thus, the current computational kneebiomechanics cannot describe the real knee biomechanicscompletely. Second, the kinematics and kinetics results fromdifferent research are vastly different. The results are hard toapply in the designing knee assistive devices and optimizingrehabilitation exercise program directly. Therefore, the kine-matics and kinetics analyses must be redone in actual use.Third, the studies about the biomechanical influences ofknee disorders are mainly concentrated in walking. Littleresearch has been done on other daily life activities, suchas running, stair climbing, and sit-to-stand. Fourth, there isan insufficient recognition of the influence of disorders onthe knee biomechanics. The influence will always beobtained by patients-normal comparative experiments.And there is severe shortage of deeper rational analyses ofthe influence.

There are several limitations of our review. First, onlyarticles published in English were included posing a languagebias to article selection. Second, the review findings are lim-ited to the articles identified by the set search strategy. Third,the quality of evidence for each study was very low because ofthe study designs and high heterogeneity.

In the future, the biomechanics of the normal anddiseased knee joint will constitute a key research direc-tion. More realistic biomechanical models and computingmethods will be further developed for a deeper under-standing of the kinematics and kinetics of the knee joint.And more rational analyses about the biomechanical influ-ences of knee disorders will be further established to designbetter assistive mechanisms.

Conflicts of Interest

The authors have no conflicts of interest to declare.

Acknowledgments

The research is supported by the Fundamental Research Fundsfor the Central Universities (Grant No. 31020190503004)and the 111 Project (Grant No. B13044).

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